FGFR1 and Chronic Eosinophilic Leukemia, Not Otherwise Specified: In 2008, in response to the identification of patients with “chronic eosinophilic leukemia” or “hypereosinophilic syndrome” who carried recurrent tyrosine kinase fusion genes involving PDGFRA, PDGFRB, or FGFR1, the World Health Organization classification of myeloid neoplasms included a new category termed “Myeloid/lymphoid neoplasms (MLN) with eosinophilia and rearrangements of PDGFRA, PDGFRB, or FGFR1” [1].